It's fairly harmless and can be ignored,
as discussed here.
It has been occurring in OpenEJB since Sun JDK 1.6 update 18 and will hopefully disappear in a future release of OpenEJB or the JDK.

org.apache.tapestry5.internal.services.TransformationException: Unable to add new method public final java.lang.xxxxx getYyyyy() as it already exists.
A field that has been annotated with @Property also has a getter or setter.
Since Tapestry 5.0.16 this has been flagged as an error (and quite rightly, too).

HTTP Status 404This is common if reloadable="true"
(see reloading web programs)
and you try a web page in the few seconds after modifying its class.
Tomcat is just reloading the class.
If you then press the Back button and try again you will usually succeed.

[[missing key:
The component cannot find a message with the key that is shown after the ":", either because it is missing from the relevant
properties file or the properties file is missing. eg. [[missing key: unknown-symbol]], means that the message with the key
"unknown-symbol" is missing, or the whole properties file is missing.

java.io.InvalidClassException: org.jboss.ejb3.remoting.IsLocalInterceptorCaused by client having a different version of the class than is being used
by the JBoss server.
Check jboss.dir in build.properties really is pointing to the server you're testing against.
After modifying it, re-run the get-dependent-jars target of build.xml,
then refresh the project in Eclipse and try running the test again.

"BUILD FAILED ... Could not create task or type of type: junit."Might occur when running the test target of build.xml.
By default Eclipse does not run junit in Ant even though Eclipse comes with a junit plug-in.
Ryan Lowe's blog explains how to set it up.